Conventionally, various types of variable compression ratio mechanism are known for varying a mechanical compression ratio of an internal combustion engine. For example, the present applicant and others have proposed many variable compression ratio mechanisms, each of which is configured to vary a piston top dead center position vertically by varying a link geometry of a multi-link type piston-crank mechanism. Moreover, variable compression ratio mechanisms are publicly known each of which is configured to vary a mechanical compression ratio similarly, by varying a cylinder position vertically with respect to a central position of a crankshaft.
A patent document 1 discloses an actuator apparatus for such a variable compression ratio mechanism, in which an actuator and an auxiliary shaft are provided in a housing mounted to a side wall of an engine body, and the auxiliary shaft and a control shaft inside the engine body are linked via a link mechanism. Specifically, the auxiliary shaft is configured to be rotated via a speed reduction mechanism by an actuator such as an electric motor within a predetermined angle range, to determine rotational position of the control shaft.
The housing described above is formed substantially integrally with a mount part for an oil filter in a lubricating oil system of an internal combustion engine. Specifically, the housing is employed and configured for mounting a cartridge type oil filter, because the housing projects outwardly from the side wall of the engine body.
The configuration that the oil filter mount part is formed integrally with the housing of the actuator apparatus, leads to an increase of thickness of the housing and thereby an increase of weight of the housing, for ensuring rigidity of the oil filter mount part. Furthermore, a variable compression ratio mechanism as described above is provided with a stopper part configured to be in mechanical contact with a part of the auxiliary shaft or link, and thereby define a bound of mechanical compression ratio for a lower compression ratio side or a higher compression ratio side. If this stopper part is arranged in the actuator apparatus, it may be also a factor for increasing the weight of the housing.
Since the housing is mounted to the side wall of the engine body to project outwardly, increase of the weight of the housing may adversely affect vibration and noise of the internal combustion engine, and is therefore undesirable.